The rules of the game:
1) Other states maintain their signage as current even if a route ends at the border. No more border continuity (CT-RI 216, RI-MA 81, etc.); in the case of RI-MA 114A, I presume MA would renumber to MA 89 to match my proposed RI 89. (87 and 89 are both free and would both fit.)
2) No new Interstate routes. No RI 95 to avoid conflict.
3) US 1A will be decommissioned because MA does not recognize it, and US 6A will be decommissioned because it is short and not a useful alternate to US 6. (It could be signed Business US 6 if RIDOT were so inclined.) All other US highways will cross the state border at the same points but may be rerouted (especially in the Providence area). No RI 1, 6, or 44 to avoid conflicts.
3) No new miles of road may be built. Freeways may not be upgraded from existing surface roads (e.g. upgrading RI 146 north of RI 99), but surface roads may be upgraded from town maintenance to state maintenance and standards.
4) A US highway or state route may be downgraded to a town road.
5) For my purposes, odds go N-S, evens go E-W, and numbers increase from the NW corner. Routes ending in 5 or 0 are the longest. Anything state-maintained will have a two-digit designation, including US and Interstate routes and short stubs measurable in hundreds of feet. It's up to RIDOT whether to sign a particular route or not, though I imagine the Interstate and US highway "secret routes" will go unposted because they are not continuous with the major route.
6) Any route or section of route not mentioned in the list is downgraded. Any route mentioned in the list that was town- or city-maintained (such as RI 51) is now state-maintained.